(1) Field of the Invention
The present invention relates to a multi-layered film, an electronic device, and manufacturing methods thereof.
(2) Description of Related Art
Electronic devices having features of being light, thin, less subject to splitting, bendable, and so on are realized by being formed on a plastic film. Such electronic devices are collectively called flexible electronics devices, and development of the flexible electronics devices has been actively promoted in recent years. Examples of such electronic devices include displays, photoelectric conversion elements, and RF tags. An outline of flexible displays is for example found in Flexible Flat Panel Displays, Gregory P. Crawford, 2005, Wiley.
A plastic film is more gas-permeable than a conventional glass substrate. This might cause deterioration of an electronic device due to gas permeation. In particular, moisture vapor is generally known for promoting temporal deterioration of a metal wiring, a semiconductor layer, and so on. In order to prevent this, a method of forming a gas barrier layer on a film has been adopted. For example, Specification of U.S. Pat. No. 6,866,901 discloses a configuration of alternately laminating inorganic films and organic films.
A moisture vapor transmission rate is evaluated by mass of water that transmits per unit area per day. Generally, an inorganic thin film has higher gas barrier properties than an organic thin film.
The inorganic film has a lower moisture vapor transmissivity than the organic film. This is because the inorganic film is denser than the organic film, and accordingly is less subject to permeation of gas molecule (water molecule in the case of moisture vapor) than the organic film.
In contrast, the inorganic film is generally easier to break than the organic film when bent or stressed. In the case where the organic film is split, gas barrier properties are lost. Furthermore, an electronic device formed on the film is destroyed, and as a result suffers from a fatal defect. It is generally known that the higher a density of a film is, the higher an elastic modulus of the film is, and the higher an elastic modulus of a film is, the more subject to splitting the film is.
In order to fully utilize the bendability which is an advantage of a flexible electronic device for industrial application, it is necessary to exhibit both gas barrier properties and bending tolerance of a gas barrier layer.
According to the configuration which is disclosed in Specification of U.S. Pat. No. 6,866,901, when an inorganic film is bent or stressed, a stress is spread inside the inorganic film. This configuration results in that the inorganic film is subject to splitting at a part thereof where a stress concentrates compared with a case where an organic film is used.